1. Technical Field
The presently disclosed subject matter relates to a semiconductor light emitting device. In particular, the presently disclosed subject matter relates to a semiconductor light emitting device of what is called a side view type for emitting light mainly in a direction substantially parallel to a surface on which the semiconductor light emitting device is to be held.
2. Related Art
Backlight units used in a liquid crystal display device may include backlight units of both an edge light type and those of a direct type. Thin liquid crystal display devices incorporated in cell phones, notebook personal computers, and other devices generally employ the edge light type backlight unit. According to the edge light type backlight unit, light emitted from a light source enters a light-transmitting light guide plate through a side surface of the light guide plate. Then, the traveling direction of the light is changed by using reflection dots and the like provided on a surface of the light guide plate, so that the whole surface of the light guide plate is uniformly illuminated. This surface light emission constitutes backlight units of liquid crystal display devices.
Light sources for use in the edge light type backlight unit include light emitting diodes (LEDs) for compact liquid crystal display devices such as those used in cell phones, as well as cold-cathode tubes (CCLFs). LEDs for use in the edge light type backlight unit can be what are called side view type LEDs each having a light emitting surface extending in a direction substantially perpendicular to a surface on which an LED package is mounted.
FIG. 1 shows an exemplary structure of a conventional side view type semiconductor light emitting device. The conventional side view type semiconductor light emitting device can include a first substrate 100 with electrodes formed on its surface, an LED chip 110 mounted on the first substrate 100, a spacer 120 provided on the first substrate 100, a second substrate 130 facing the first substrate 100 with the spacer 120 interposed therebetween, and a light-transmitting resin 140 applied to fill a space defined by the first and second substrates 100 and 130 and by the spacer 120, the light-transmitting resin 140 burying the LED chip 110. (See, for example, Japanese Patent Application Laid-Open No. 2007-59612.)
The semiconductor light emitting device of the conventional structure has suffered from the deviation of directional characteristics of light emitted from a light emitting surface 300. FIG. 2 shows directional characteristics of the conventional side view type semiconductor light emitting device described above, and describes the proportion of light intensity as viewed in an angle range of θ degrees with respect to a light source when the axial light intensity is 100%. As shown in FIG. 2, light emitted from the light source does not spread symmetrically in a horizontal direction (or optical axis). Rather, the intensity of the light tends to decrease in a region below a surface on which the LED chip 110 is mounted (in a region closer to a surface 200 on which the semiconductor light emitting device is to be held), and tends to increase in a region above that surface. This is because light emitted from the LED chip 110 toward the surface 200 is reflected off a surface of the first substrate 100 as shown in FIG. 1. These directional characteristics of light reduces efficiency of light entry into a light guide plate, by which nonuniformity of brightness may be generated in the surface of the light guide plate.